The present invention pertains to nuclear fuel rods for use in nuclear reactors and, more particularly, to a device for aligning nuclear fuel pellets so as to facilitate subsequent filling of fuel rods with the pellets.
In a typical nuclear reactor, the reactor core includes a large number of fuel assemblies, each of which is composed of a multiplicity of elongated fuel elements or rods. The fuel rods each contain fissile material in the form of a plurality of generally cylindrical nuclear fuel pellets stacked within a hollow tube. The pellets, which are formed of a sintered metal oxide, are rather fragile and are subject to cracking and chipping. Use of cracked or chipped pellets may result in localized operating abnormalities within the reactor core and, therefore, must be avoided. For this reason, the pellets must be carefully inspected before being loaded or inserted into the tubes to form fuel rods. The inspection process is complicated by the fact that the pellets are, of course, radioactive. This requires that the duration of human exposure to the pellets be minimized. A further problem is presented by any chips or fragments which may separate from the pellets during inspection and preparation for loading. All such chips and fragments must be captured for appropriate disposal or they will constitute a serious impediment to entry of the pellets into the tube.
It is, therefore, a primary object of the present invention to provide a device for axially aligning nuclear fuel pellets while avoiding or minimizing damage thereto.
It is a further object to provide such an alignment device which advantageously includes means for separating and collecting any chips or other fragments which may become detached from the bodies of the pellets.
It is yet another object to provide such an alignment device which advantageously includes means for rotating the aligned pellets, to facilitate visual inspection of their circumferential surfaces, without disturbing their axial alignment.
The foregoing and other objects as may hereinafter appear are achieved by an aligning device comprising a grooved, vibrating table and a conveyor assembly for receiving fuel pellets and depositing them on the table. More specifically, the table surface is formed with a plurality of parallel grooves each comprising a pair of inclined, planar side surfaces and a curved bottom surface. The conveyor assembly includes a horizontal traveling belt, onto which the pellets are poured from a container, and an inclined planar slide communicating between the belt and the grooved surface of the table. The conveyor assembly is movably supported for reciprocating motion above the oscillating table to facilitate the deposit of the pellets thereon in a single layer.
Advantageously, the aligning device includes an inspection station comprising a frame, disposed adjacent the vibrating table, which supports a plurality of elongate cylindrical rollers in parallel, spaced relation. The cylindrical rollers loosely rest on a plurality of grooved rollers, rotatably mounted on the frame and rotated in unison by a drive chain and motor. Aligned pellets from the oscillating table are delivered onto the cylindrical rollers where they are caused to slowly rotate about their longitudinal axes, thereby presenting their entire circumferential surfaces for visual inspection.
A control member is transversely disposed between the oscillating table and the inspection station. The control member is displaceable between a first position, whereat a column of aligned pellets may be transferred from the table to the inspection station, and a second position, whereat such transfer is prevented.
A plurality of trough members are provided, each adapted to receive a single column of aligned pellets. A locking member, on the distal end of the inspection station, releasably secures the trough members in columnar-flow communication therewith. The aligned and inspected pellets are transferred to the trough members and, thereafter, the individual trough members are taken to a loading station whereat the pellets are inserted into fuel rods.